The present invention relates to a spray booth with improved electrostatic disk. It is known that spray booths are provided for coating for example metallic panels and allow to introduce the panel and pass it, by following an appropriate path, around at least one electrostatic disk provided to coat the panel.
Conventionally, the electrostatic disk can move along a vertical shaft whose axis is parallel to the vertical axis of the spray booth. The upward or downward translational motion of the electrostatic disk allows to coat the panel at all of its regions, also taking into account the fact that the panel follows a complex path around the electrostatic disk, so as to make both of its sides face the rim of said electrostatic disk.
The electrostatic disk is circumferentially provided with a plurality of electrodes that protrude radially from it and allow to generate an electrical field by virtue of which adhesion between the paint powder and the panel to be coated is produced.
FIG. 1 is a sectional view of an electrostatic disk, designated by the reference numeral 1, which can perform a translational motion along a shaft 2. The disk is provided with a plurality of electrodes 3 that protrude radially from it and is coupled to a base element 4 that is rigidly coupled to the shaft 2, forming between its lower surface and said base element 4 a chamber 5 that is directly connected to the outside environment by virtue of a channel 6 that is arranged adjacent to the shaft 2.
The paint powders by means of which the piece being processed is to be coated are introduced through the channel 6. The powder then passes through the chamber 5, and by virtue of the presence of pressurized air it is injected through a slit 7 that exits at the lower side of the electrodes 3.
The injection of air to push the paint powder through the slit 7 causes said powder to adhere to the surface of the panel to be coated by virtue of the presence of an electrical field generated by a voltage source connected to the upper surface of the electrostatic disk 1.
However, the above proposed solution has several constructive drawbacks. First of all, the presence of a high voltage of the electrodes, for example approximately 50 kV, triggers electrical discharges between the electrodes and the piece to be coated, since said panel, due to oscillations caused by its movement around the electrostatic disk 1, sometimes tends to move excessively close to said electrostatic disk.
The oscillations caused by the movement of the panel therefore reduce considerably the coating distance, consequently triggering electrical discharges between the electrodes and the panel.
Currently, safety is ensured by a threshold system that limits the maximum value of the current that can flow through the electrode, thus reducing the possibility of triggering the discharges.
Every time the current exceeds the preset maximum threshold value, the control system stops the unit.
However, since oscillations of the panels are quite frequent, and since the reduction of the useful distance between the panel and the electrodes entails the triggering of electrical discharges, there are many unit stoppages when the above described threshold system is used.
Another known type of control system uses a feedback control that allows to keep the power level constant, reducing the voltage as the current increases. However, said control system is not rapid enough to avoid the electrical discharge once it has been triggered.
Currently, the statutory provisions that govern the safety of spray booths entail, for the power levels involved, the adoption of a fire-fighting system. This naturally complicates considerably the construction of the spray booth in addition to increasing its costs.
Furthermore, the electrodes that generate the electrical field for the electrostatic deposition of paint powders on the panel to be coated lose their efficiency over time, since there is a strong adhesion of powder to the surface of the electrode, reducing its efficiency.
For this purpose, in order to improve penetration in cavities or recesses of the piece to be coated, powders with a smaller than normal particle size are used, accordingly requiring custom production. This entails a cost problem that increases as the size of the batch to be coated decreases and therefore the required amount of powders decreases.
The aim of the present invention is to provide a spray booth with improved electrostatic disk, which allows to reduce considerably the possibility of triggering electrical discharges between the electrodes and the surfaces of the pieces to be coated.
Within the scope of this aim, an object of the present invention is to provide a spray booth with improved electrostatic disk that allows to reduce drastically system stoppages caused by the triggering of discharges between the electrodes and the surfaces of the pieces to be coated.
Another object of the present invention is to provide a spray booth with improved electrostatic disk that does not require fire-fighting systems because the power levels generated are contained within preset limits set by currently applicable statutory provisions.
Another object of the present invention is to provide a spray booth with improved electrostatic disk that does not require the use of coating powders having a particular particle size in order to achieve satisfactory penetration in the cavities of the piece to be coated.
Another object of the present invention is to provide a spray booth with improved electrostatic disk that is highly reliable, relatively simple to provide, and at competitive costs.